Several lines of research have suggested that cardiovascular reactivity to stress may be a risk factor for cardiovascular diseases--i.e., hypertension and coronary heart disease. Although most studies have evaluated reactivity in the laboratory, there is substantial evidence that cardiovascular patterns under naturalistic circumstances in the field are highly correlated with risk for disease. Therefore, the modification of cardiovascular reactivity to stress in the lab and field by behavioral means may contribute to the prevention of cardiovascular disease and its complications. Previous studies in the behavioral treatment of reactivity have been significantly flawed in control for confounding variables such as expectancy, design, and duration of treatment. There has been little or no previous research on the